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Life, Unbounded

Life, Unbounded


Discussion and news about planets, exoplanets, and astrobiology
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We All Carry Stardust Memories

The views expressed are those of the author and are not necessarily those of Scientific American.


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The Trifid Nebula - a potential analog for the kind of place our Sun was formed in 4.5 billion years ago (NASA/ESA)

In lieu of a proper post I thought I’d link to a recent video courtesy of SpaceLab at YouTube. In it you can watch a rather unshaven and scraggly version of me answering a simple but terrific question about the debt we owe to stellar nucleosynthesis. This issue also leads us to think about the other stars that formed from the same clumps of heavy-element enriched material that our solar system condensed out of, since any worlds around those long-lost sisters could contain the very same elemental spice as us. Somewhere out there in the galaxy there might just be other organisms connected to us through the massive stars that forged our common mix of oxygen, carbon, nitrogen and everything else – the ultimate stellar gene-pool.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. Postman1 4:41 pm 10/6/2012

    It would be nice if we could someday ‘run it all backwards’ and figure out where those sister stars are now. I don’t expect we ever will, too many variables, but those would be great places to look for planets or signs of ETI.

    Link to this
  2. 2. Postman1 8:46 pm 10/7/2012

    Caleb, I may just be running in circles and confusing myself, but the following questions keep coming to me:
    If the space between two specific galaxies is expanding, how does that affect the speed of the photons traveling from one to the other? Are they stretched out by the expansion, do they slow down so as not to exceed the speed of light, or do they speed up due to the expansion?
    How will each one of the above affect the red shift as observed from each galaxy? If the red shift were increased, would it appear that the galaxies are moving away from each other faster than they really are? And, if so, would there be an exponential effect, making it appear that expansion is accelerating?
    Does anyone know the answers to these questions?

    Link to this
  3. 3. Caleb A. Scharf in reply to Caleb A. Scharf 9:25 am 10/15/2012

    The photon wavelength gets stretched, i.e. their energy is lowered during transit through expanding space. If you translate this shift in wavelength (as a Doppler shift) to an effective velocity of (for example) a distant galaxy you will indeed find that velocity can exceed the speed of light. But it’s the *space* expanding, nothing is moving FTL in its local reference frame. The relationship between this ‘recession’ velocity and physical distance is given by Hubble’s Law, which is linear locally (v=HD) but curved over larger distances/cosmic time.

    Link to this

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